Finely chop the chocolate and place it in a bowl over simmering water. Stir to melt the chocolate evenly. Remove the chocolate from the water when three-quarters melted and stir until all the pieces have melted. Stir in all the corn syrup with a rubber spatula at once. Continue to stir until the chocolate starts to leave the sides of the bowl. For dark chocolate, this takes about 60 seconds. For white or milk chocolate, the process takes about 20 to 30 seconds.

Scrape the chocolate mixture onto a piece of plastic wrap. Spread out the chocolate about 1/4 to 1/2 in. (6 mm to 1.3 cm) thick. Place another piece of plastic wrap on top of the chocolate. Refrigerate or rest in a cool, dry place to age for 24 hours.

Once aged, cut the chocolate plastic into smaller pieces and microwave pieces for a few seconds just to take the hard edge off the chocolate. Knead thoroughly with the heel of your hands until the chocolate has elasticity and a shiny coat. Wrap in plastic wrap until ready to use. Will last for several weeks in a cool dry room.

Note: Corn syrup and molasses are heavier than thinner liquids like water, milk, and juice. Instead of measuring roughly the same number of ounces in volume and weight, the weight will be 1-1/2 times the volume. Thus, 4 fl oz (118 ml) of corn syrup will weigh not 4 oz (114 g) but 6 oz (168 g).